Tamper evident closures for containers

ABSTRACT

A cap ( 10 ) including a transverse end wall ( 12 ) and a skirt ( 14 ) is disclosed. The skirt ( 14 ) is divided by a line of weakening ( 24, 26 ) into a main part ( 22 ) and a band ( 20 ). At least the band ( 20 ) is of heat shrinkable material. When the band is heated after fitting to the container ( 18 ) it pulls in under a bead ( 36 ) which encircles the container&#39;s neck.

FIELD OF THE INVENTION

THIS INVENTION relates to tamper evident closures for containers such asbottles.

BACKGROUND TO THE INVENTION

The most commonly used type of tamper evident threaded closure has aseries of protrusions which project inwardly from a skirt and interlockwith a bead of the container. The protrusions are on a band which formspart of the skirt and which is joined along a line of weakening to theremainder of the skirt. The band itself has a transverse line ofweakening extending across it. It is intended that any attempt to removethe cap causes the band to break along its transverse line of weakening.However, it is possible with care to remove such a closure withoutdamaging it, and then screw it back onto the bottle again withoutdamaging it. It consequently does not reveal tampering.

The present invention provides an improved tamper evident closure.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention there is provided amethod of manufacturing a cap for closing a container, the methodcomprising moulding the cap with a skirt which is subdivided by acircumferentially extending line of weakening into a main part and aband, at least the band being of heat shrinkable material.

The method of manufacturing can comprise moulding the cap andsubsequently expanding the moulded band thereby to increase itsdiameter.

The band can be expanded mechanically by means of movable components ofthe mould, or can be subjected to air pressure which expands the band.

According to a second aspect of the present invention there is provideda cap which comprises a transverse end wall and a cylindrical skirt, anend portion of the skirt being in the form of a band which is connectedto the skirt along a line of weakening, the band being of heatshrinkable material.

According to a third aspect of the present invention there is provided amethod of closing a container which comprises fitting a cap as definedabove onto the container, and subjecting the band to heating to shrinkit onto the container.

According to a fourth aspect of the present invention there is provideda tamper evident cap which comprises a transverse end wall and acylindrical skirt, the end portion of the skirt being in the form of aband joined to the remainder of the skirt by a series of bridges, theband having been stretched during manufacture and being of a materialwhich shrinks when it is heated.

According to a fifth aspect of the present invention there is provided atool for use in the manufacture of a tamper evident cap, the toolcomprising a female mould and a mandrel which together define a mouldcavity having the shape of the cap to be moulded, the mould cavityhaving a first part in which the greater part of the length of the skirtof the cap and a transverse end wall of the cap are moulded, a secondpart in which a band forming the end part of the skirt of the cap ismoulded, and notches arranged in a circle, the notches joining thecavity parts and a series of bridges between the band and the remainderof the skirt being moulded in these notches, the inner diameter of atleast a portion of the subsidiary cavity part being less than the innerdiameter of at least a portion of the main cavity part.

According to a sixth aspect of the present invention there is provided amethod of moulding a cap which comprises feeding synthetic plasticsmaterial to a mould cavity defined between surfaces of a mandrel andsurfaces of a female mould, the mould cavity having the shape of the capto be moulded, the mould cavity having a first part in which the greaterpart of the length of a skirt of the cap and a transverse end wall ofthe cap are moulded, a second part in which a band forming the end partof the skirt is moulded, and notches arranged in a circle and which jointhe cavity parts, the inner diameter of at least a portion of thesubsidiary cavity part being less than the inner diameter of at least aportion of the main cavity part, and removing the moulded cap from themandrel in such manner that the band is stretched as it passes over thepart of the mandrel which defines the first part of the mould cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how thesame may be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings in which:

FIG. 1 is a section through a cap at an intermediate state in themoulding procedure;

FIG. 2 is a similar section showing the cap at a later stage in themoulding procedure;

FIG. 3 is a pictorial view showing the cap being presented to a bottlefor fitting;

FIG. 4 is a pictorial view showing the cap on the bottle;

FIG. 5 is a diagrammatic section, to a larger scale, showing the cap andbottle of FIG. 4;

FIG. 6 is a view similar to that of FIG. 4 and showing the cap afterheat treatment;

FIG. 7 is a diagrammatic section similar to that of FIG. 5 and showingthe cap after heat treatment;

FIG. 8 is a section through a further cap;

FIG. 9 is an axial section through a closed tool for use inmanufacturing the cap of FIG. 8;

FIG. 10 shows the tool immediately after it has been opened; and

FIGS. 11 a, 11 b and 11 c are sequence drawings showing a cap beingrotated off a mandrel forming part of the tool of FIGS. 9 and 10.

DETAILED DESCRIPTION OF THE DRAWINGS

The cap 10 shown in FIGS. 1 to 7 comprises a transverse end wall 12 anda skirt 14. The skirt has internal threading at 16 which matchesexternal threading of the neck (see FIGS. 5 and 7) of a container 18which, in the illustrated embodiment, is in the form of a bottle.

The free end portion of the skirt 14 is in the form of a band 20. Theband is joined to the main part 22 of the skirt 14 by a series ofcircumferentially spaced bridges 24. The effect of this is to provide acircumferentially extending line of perforations 26 which alternate withthe bridges 24. The line of perforations 26 is interrupted by anon-perforated zone 28 (FIGS. 2 and 3) at which the band 20 is joined tothe main part 22 of the skirt 14. The non-perforated zone 28 constitutesa bridge which is wider than the bridges 24.

The band 20 has a line of weakening 30 which extends from the free edgethereof to the line of perforations 26. The line of weakening 30 cancomprise a series of perforations or a line where the band 20 is ofreduced thickness.

As will clearly be seen from FIGS. 5 and 7, the band 20 is thinner thanthe main part 22 of the skirt 14, and there is an internal step at 32where the change in thickness occurs.

The cap is moulded with its band 20 tapering inwardly as shown inFIG. 1. Before the cap is removed from the mould the band 20 isstretched so that it takes on the cylindrical configuration shown inFIG. 2. This can be achieved either mechanically by means of parts ofthe mould which expand forcing the still soft band 20 outwardly or byapplying air pressure. This latter method is a technique known asstretch blow moulding.

PET is the preferred material for the cap but any other heat shrinkableplastics material can be used.

If reference is now made to FIGS. 4 and 5, it will be seen that the cap10 has been screwed onto the container 18 until the free edge of theband 20 is close to the flange 34 of the container. Movement of the cap10 is limited by engagement between the bead 36 of the container and thestep 32 where the main part 22 of the skirt 14 of the cap 10 merges withthe band 20. Once the cap has been screwed onto the container as shownin FIGS. 4 and 5, the capped bottle moves into a heat shrink tunnel. Themain purpose of heating the bottle is to shrink the bottler'sconventional synthetic plastics material sleeve shaped label around thebody of the bottle. The effect of the heat on the thin band 20 is tocause it to shrink back to the condition in which it was moulded (seeFIG. 1) which results in it tightly gripping the container between thebead 36 and the flange 34 (FIGS. 6 and 7).

Experimental work has shown that the band 20, once it has shrunk ontothe container 18, is brittle. Any attempt to prise the band 20 off thecontainer causes it to fail along the weakened line 30 which extendsacross it.

The cap 10 is removed from the container 18 by twisting it. The band 20,because it is a tight fit around the neck of the container, resiststurning and the result is that the cap breaks along the line ofweakening 30. The cap 10 also breaks along the line of perforations 24and either separates from the remainder of the cap entirely or remainsattached to it by way of the zone 28 across which the line ofperforations 24 does not extend. The fact that the cap 10 has previouslybeen removed from the container is evident because the band 20 is eithermissing completely or is only attached to the remainder of the cap atthe zone 28 but broken along its axially extending line of weakening.

The cap 38 shown in FIG. 8 has a transverse end wall 40 and acylindrical skirt designated 42. The skirt comprises a main part 44 anda subsidiary part in the form of a band 46. The band 46 is joined to theskirt part 44 by way of a series of bridges 48. There are openings 50between adjacent bridges. The configuration of the cap 38 will bedescribed in more detail hereinafter. On the inside of the skirt part 44there is a helical thread 52.

The tool 54 illustrated in FIGS. 9 and 10 comprises a female mould 56and a male mandrel 58. The mould 56 comprises two parts designated 60,62.

The mould 56 has a cavity 64 (see particularly FIG. 10) bounded by atransverse end surface 66 and a cylindrical side surface 64.

The part 62 of the female mould 56 has a runner 66 through it and asprue 68 connecting the runner 66 to the cavity 64 of the mould 56.

The mandrel 58 comprises a cylindrical core 70 with a stem 72 protrudingfrom it. The mandrel 58 also comprises a rod 74 which is co-axial withthe core 70 and the stem 72 and is both rotatable and axially shiftablerelative thereto. The final component of the mandrel 58 is a ring 76which encircles the core 70 and the stem 72.

The core 70 and rod 74 define a composite end surface 78 which faces thesurface 66 of the female mould 56. The core 70 also has a cylindricalside surface 80 which faces the surface 64 of the mould 56. The surface80 has one or more helical grooves 82 cut into it.

The surfaces 66, 78 are parallel and spaced apart. Likewise the surfaces64 and 80 are parallel and spaced apart.

The surface 80 of the core 70 intersects a conical surface 84 of thecore along a circular line of intersection 86. The surface 84 tapersfrom the circular line of intersection 86 towards a flat, annularsurface 88 where the stem 72 protrudes from the core 70.

The ring 76 has a bore 90 through it. The bore 90 has an inner surface92 which tapers at an angle which is somewhat less than the angle oftaper of the surface 84. Thus the surfaces 84 and 92 diverge from oneanother in the direction away from the circular line 86. The surface 92extends from one end face 94 of the ring 76 to an internal transversesurface 96. The tapering surface 92 has a series of notches 98 thereinimmediately adjacent the end face 94.

When the mould is closed, as shown in FIG. 9, the circular edge 86touches the surface 92 of the ring 76. This divides the mould cavity(see FIG. 9) into a main part, designated MP1, and a subsidiary part,designated MP2, which are only in communication with one another throughthe notches 98. The greater part of the length of the skirt of the capand a transverse end wall are moulded in part MP1 and a band forming theend part of the skirt of the cap is mounted in part MP2.

The end of the rod 74 is formed with a cross shaped indentation 100 (seeparticularly FIG. 11 c).

Synthetic plastics material of a type which can be shrunk by theapplication of heat is injected through the runner 66 and sprue 68. PET(polytetrafluoroethylene) is a suitable material.

The main cavity part MP1 fills with material which eventually flowsthrough the notches 98 and into the subsidiary cavity part MP2.

Once the injected material has set, the mould is opened by separatingthe mould 56 and mandrel 58. The mandrel 58, but not the mould 56, isshown in FIG. 1l a with a cap 38 on the mandrel 58.

To eject the cap 38, the ring 76 is displaced axially with respect tothe core 70. Such linear motion is converted by threading or othersuitable means to rotary and translational motion of the rod 74. The cap38 and rod 74 are at this time interconnected due to the plasticsmaterial in the indentation 100.

Thus the cap 38 is turned with respect to the core 78 (FIG. 11 b) and iseventually screwed off the stationary core 70 by virtue of the helicalthread 52 which the threading 82 has moulded into the inside surface ofthe skirt 42 of the cap (see FIG. 8). As will clearly be seen from FIG.10, the band 46 has to be expanded outwardly to permit the cap to betaken off the core 70 of the mandrel 58. The band 46 is thus stretchedduring manufacture and consequently, at the time the cap reaches thebottling plant, the band 46 is cylindrical and forms an extension of themain part 44 of the skirt 42.

Once the cap has been screwed onto a container and then heated, the band46 shrinks back to its unstretched condition (as shown in FIG. 8) andtightly grips the container. Re-heating makes the band 46 and bridges 48brittle. There is usually a protruding circumferentially extending beadbetween the open mouth of the container and the band, and the band pullstightly under this bead.

Experimental work shows that the band splits axially, and/or all thebridges break, immediately any attempt is made to remove the cap fromthe container.

lt is possible to omit the runner and sprue and to use the techniqueknown as compression moulding to manufacture the cap. Specifically acharge of plastics material is fed into the open cavity 64 and the mouldis then closed to force material into the parts MP1 and MP2 of the mouldcavity and into the notches 98 which join the cavity parts.

To facilitate removal of the cap from the mandrel, the core 70 can tapervery slightly from top to bottom (as viewed in FIG. 10). Similarly, thethread 82 can taper so that its dimensions reduce in the top to bottomdirection.

1. A method of manufacturing a cap for closing a container, the methodcomprising moulding the cap with a skirt which is subdivided by acircumferentially extending line of weakening into a main part and aband, at least the band being of heat shrinkable material.
 2. A methodas claimed in claim 1 and including the step of expanding the mouldedband thereby to increase its diameter.
 3. A method as claimed in claim2, wherein the band is expanded mechanically by means of movablecomponents of the mould.
 4. A method as claimed in claim 2, wherein theband is subjected to air pressure to expand it.
 5. A cap which comprisesa transverse end wall and a cylindrical skirt, an end portion of theskirt being in the form of a band which is connected to the main part ofthe skirt along a line of weakening, the band being of heat shrinkablematerial.
 6. A method of closing a container which comprises fitting acap as claimed in claim 5 to the container, and subjecting the band toheating to shrink it onto the container.
 7. A tamper evident cap whichcomprises a transverse end wall and a cylindrical skirt, the end portionof the skirt being in the form of a band joined to the remainder of theskirt by a series of bridges, the band having been stretched duringmanufacture and being of a material which shrinks when it is heated. 8.A tool for use in the manufacture of a tamper evident cap, the toolcomprising a female mould and a mandrel which together define a mouldcavity having the shape of the cap to be moulded, the mould cavityhaving a first part in which the greater part of the length of the skirtof the cap and a transverse end wall of the cap are moulded, a secondpart in which a band forming the end part of the skirt of the cap ismoulded, and notches arranged in a circle, the notches joining thecavity parts and a series of bridges between the band and the remainderof the skirt being moulded in these notches, the inner diameter of atleast a portion of the subsidiary cavity part being less than the innerdiameter of at least a portion of the main cavity part.
 9. A method ofmoulding a cap which comprises feeding synthetic plastics material to amould cavity defined between surfaces of a mandrel and surfaces of afemale mould, the mould cavity having the shape of the cap to bemoulded, the mould cavity having a first part in which the greater partof the length of a skirt of the cap and a transverse end wall of the capare moulded, a second part in which a band forming the end part of theskirt is moulded, and notches arranged in a circle and which join thecavity parts, the inner diameter of at least a portion of the subsidiarycavity part being less than the inner diameter of at least a portion ofthe main cavity part, and removing the moulded cap from the mandrel insuch manner that the band is stretched as it passes over the part of themandrel which defines the first part of the mould cavity.